In one known method for measuring the configuration, dimension etc. of, for example, a large-sized structure such as a bridge girder, target marks, reflection seals or the like are affixed to all measuring points in the measuring object and these target marks are sighted for measurement by the workman through an angle measuring instrument such as a transit or through an optical distance measuring instrument.
Another known measurement method is carried out with the arrangement illustrated in FIG. 15 in which a movable portal structure 102 is so disposed as to straddle across a measuring object 100 and to travel along guide rails 101 which extend in parallel with the measuring object 100. A hand 103 having a measuring instrument 104 at its leading end is mounted on the portal structure 102 and the portal structure 102 travels along the guide rails 101, while measuring the measuring object 100 by means of the measuring instrument 104.
Japanese Patent Publication No. 60-196615(1985) discloses still another known method in which an image pick-up device (i.e., angle measuring instrument) travels along guide rails extending in parallel with a measuring object and measurement is made utilizing triangulation.
The above method using target marks or the like has the disadvantages that affixing of target marks to all measuring points in a measuring object is troublesome and that visual inspection of these target marks causes lots of fatigue to the workman and is very time-consuming.
The method illustrated in FIG. 15 requires a large-sized fixed equipment and therefore large installation space. Since this method has to meet the conflicting requirements, that is, the installation of large-sized equipment and high accuracy, the measurement cost inevitably increases.
The method disclosed in the above Japanese Publication requires another set of guide rails laid on the rear side of the measuring object in order to install the image pick-up device. This also creates a need for large-sized fixed equipment, entailing an increase in the cost of the overall system.
The present invention has been made with a view to solving the foregoing problems and one of the objects of the invention is therefore to provide a structure measurement system which can be economically formed as it requires no large-sized fixed equipment nor large installation space and which can reduce the workman's burden by minimizing the work of affixing target marks or the like.